The forestay can probably be removed from the CDI, any CDI I have worked on it could be removed. If the foil on the new furler will allow the fitting on the end of the forestay to pass through it may be possible to reuse it.
Probably only a good idea if it fairly new, it is a critical part of your rigging with no backup if it fails so might want to replace that part anyways.
The new furler will specify a "tape size" in the manual, like #5 or #6 or #7 luff tape. This is the round piece sew on the luff of the sail that slides up inside the groove in the furler foil.
In my experience the CDI furlers have very generous grooves for the luff tapes and I have never had a problem with them. Some other manufactures have very tight tolerances on the luff tape size and it may need to be changed on your sail. Sometimes it even needs to be changed on a new sail that was made to fit that furler, been there done that.
Often the sail loft can release the line inside the luff tape and pull a smaller line up inside the tape to match what your your foil needs. A very inexpensive fix.
If I recall correctly the tape number is supposed to be the diameter of the line in 32nds of an inch used to make the tape. A #6 tape is made with a 6/32" line.
So you should be able to measure the diameter of the luff tape on your sail, look up size required in the new the furler manual and know if it will fit. I did all that and it still did not fit ! so no guarantees, just saying that is how it is supposed to work.........
good luck, Bob